NaN means Not a Number. The library did not receive a valid reading from the sensor.

It is accurate enough for beginner weather and room projects, but not for calibrated laboratory measurement.

DHT22 Temperature & Humidity Sensor — Component Guide

Q: What does the DHT22 measure?

It measures air temperature and relative humidity. It does not measure pressure, gas, dust, rain, soil moisture, or water temperature.

Q: Is DHT22 digital or analog?

It is digital. The ESP32 reads timed HIGH and LOW pulses on one GPIO pin, so analogRead() is not used.

Q: Can I connect DHT22 directly to ESP32?

Yes. Use 3.3 V, GND, and one GPIO data pin. Add a pull-up resistor if your sensor board does not already include one.

Q: Can I power DHT22 from 5 V?

Avoid 5 V for direct ESP32 projects unless you are certain the DATA pull-up remains at 3.3 V. ESP32 GPIO pins are not 5 V tolerant.

Q: Which GPIO is best for DHT22 on ESP32?

GPIO4 is a good beginner choice. Many normal GPIOs work, but avoid boot strapping pins until you understand ESP32 boot behavior.

Q: Why do I need a pull-up resistor?

The data line must idle HIGH. The resistor pulls DATA to 3.3 V until the sensor pulls it LOW to send timed bits.

Q: What resistor value should I use?

10 k ohm works well for short breadboard wires. For longer wires, 4.7 k ohm may be more reliable.

Q: How often can I read DHT22?

Read it about once every 2 seconds. Faster reads can return NaN, repeated values, or unstable output.

Plain-English Overview

The DHT22 is a small digital sensor that reports two things about the air: temperature and humidity.

Temperature tells you how warm the air is. Humidity tells you how much water vapor is in the air. The ESP32 asks the DHT22 for a reading through one data wire, and the sensor replies with numbers your code can print, display, log, or use to control another device.

Use it when you need a simple low-cost room sensor. Do not use it for fast control loops, outdoor weatherproof measurements, or scientific calibration work.

Where You Use It

Room comfort monitor
ESP32 weather station
Greenhouse humidity monitor
Smart thermostat input
Classroom environmental data logger
Fan or ventilation trigger

Quick Facts

Measures Air temperature and relative humidity
Signal type Single-wire digital data
Update speed About one new reading every 2 seconds
ESP32 voltage 3.3 V recommended
Best beginner pin GPIO4
Library Adafruit DHT sensor library

How It Works

The DHT22 is not an analog temperature sensor. Inside the package, a humidity sensing element changes electrically as it absorbs or releases water vapor from the air. A temperature sensor measures the surrounding air temperature. A tiny controller inside the DHT22 converts those measurements into a digital data frame.

Communication happens on one DATA wire. The ESP32 briefly pulls the line low to request a measurement. The DHT22 then responds with timed HIGH and LOW pulses. Short and long pulses represent binary data. The Arduino library measures those pulse widths, checks the packet, and returns floating-point temperature and humidity values.

The pull-up resistor is important because the DATA line must normally rest at 3.3 V. The sensor transmits by pulling the line low at precise times. Without a pull-up, the line can float, noise can look like data, and the library may return NaN.

The sensor is slow because humidity measurement depends on the physical sensing material settling. That is why a 2 second interval is a requirement, not just a suggestion.

Technical Specifications

Arduino library: DHT sensor library by Adafruit plus Adafruit Unified Sensor

Specification	Value	Why it matters
Supply voltage	3.3 V to 5 V sensor range; use 3.3 V with ESP32	ESP32 inputs must not receive 5 V logic from a pulled-up data line.
Temperature range	-40 C to 80 C	Wide enough for rooms, greenhouses, sheds, and many school experiments.
Temperature accuracy	Typically +/-0.5 C	Good for learning and comfort monitoring, not for laboratory calibration.
Humidity range	0 to 100 percent RH	Covers dry indoor air through very humid environments.
Humidity accuracy	Typically +/-2 percent RH to +/-5 percent RH	Enough to detect trends, but values should not be treated as precision instruments.
Communication	Proprietary one-wire digital protocol	It uses one GPIO, but it is not Dallas OneWire and does not use I2C or SPI.
Sampling period	2 seconds minimum between reads	Reading faster commonly causes NaN or repeated values.
Resolution	0.1 C and 0.1 percent RH reported by common libraries	Displaying one decimal place is useful; extra decimals are not meaningful.
Typical current	Around 1 mA while measuring, much lower when idle	Suitable for small USB projects, but deep-sleep battery designs need careful duty cycling.
Pull-up resistor	4.7 k ohm to 10 k ohm from DATA to 3.3 V	The data line must rest HIGH so the sensor can pull it LOW to transmit bits.
Cable length	Keep breadboard wires short; long cables need stronger wiring discipline	The timing protocol is sensitive to noise and capacitance on the data line.
Best environment	Clean air, no direct water, no condensation	Moisture on the board or sensor can corrupt readings and damage electronics.

Pinout

VCC / + Power input ESP32 3.3 V Use 3.3 V for direct ESP32 wiring. Some modules accept 5 V, but 3.3 V keeps the data line safe.
DATA / OUT Digital signal output/input ESP32 GPIO4 Needs a pull-up to 3.3 V. Many modules include it; bare sensors usually do not.
NC No connection on bare 4-pin sensor Leave disconnected Some 3-pin modules do not expose this pin.
GND / - Ground reference ESP32 GND Ground must be common with the ESP32 or the data signal has no reference.

Wiring Diagram

A DHT22 module is the easiest version for beginners because it usually includes the pull-up resistor. A bare 4-pin DHT22 needs one extra resistor from DATA to 3.3 V.

Keep the wires short on a breadboard. Long jumper wires can add noise and capacitance, which makes the timed digital pulses harder for the ESP32 to read.

Wiring Diagram DHT22 VCC to ESP32 3.3 V, GND to ESP32 GND, DATA to ESP32 GPIO4, optional 10 k ohm pull-up from DATA to 3.3 V

1
Unplug the ESP32 USB cable before wiring.
2
Put the DHT22 module on the breadboard with each pin in a separate row.
3
Connect VCC or + to ESP32 3.3 V.
4
Connect GND or - to ESP32 GND.
5
Connect DATA or OUT to ESP32 GPIO4.
6
If using a bare 4-pin sensor, connect a 10 k ohm resistor between DATA and 3.3 V.
7
Leave NC disconnected on a bare DHT22.
8
Plug in USB and make sure the code uses DHTPIN 4.

Code Examples

Use the same wiring with Arduino IDE, PlatformIO, or ESP-IDF. Start with Arduino, then graduate when you need a larger project structure.

dht22_esp32_component_test.ino

#include "DHT.h"

// DHT22 DATA pin connected to ESP32 GPIO4.
#define DHTPIN 4
#define DHTTYPE DHT22

// Read slowly. The DHT22 needs about 2 seconds per fresh reading.
const unsigned long READ_INTERVAL_MS = 2000;

DHT dht(DHTPIN, DHTTYPE);
unsigned long lastReadTime = 0;

void setup() {
  Serial.begin(115200);
  delay(1000);

  dht.begin();
  Serial.println("DHT22 component test");
  Serial.println("Check wiring if you see failed readings.");
}

void loop() {
  if (millis() - lastReadTime < READ_INTERVAL_MS) {
    return;
  }
  lastReadTime = millis();

  float humidity = dht.readHumidity();
  float temperatureC = dht.readTemperature();
  float temperatureF = dht.readTemperature(true);

  if (isnan(humidity) || isnan(temperatureC) || isnan(temperatureF)) {
    Serial.println("Read failed: check DATA pin, pull-up resistor, power, and ground.");
    return;
  }

  float heatIndexC = dht.computeHeatIndex(temperatureC, humidity, false);

  Serial.print("Temperature: ");
  Serial.print(temperatureC, 1);
  Serial.print(" C / ");
  Serial.print(temperatureF, 1);
  Serial.print(" F  |  Humidity: ");
  Serial.print(humidity, 1);
  Serial.print(" %  |  Heat index: ");
  Serial.print(heatIndexC, 1);
  Serial.println(" C");
}

src/main.cpp

#include <Arduino.h>
#include "DHT.h"

// DHT22 DATA pin connected to ESP32 GPIO4.
#define DHTPIN 4
#define DHTTYPE DHT22

// Read slowly. The DHT22 needs about 2 seconds per fresh reading.
const unsigned long READ_INTERVAL_MS = 2000;

DHT dht(DHTPIN, DHTTYPE);
unsigned long lastReadTime = 0;

void setup() {
  Serial.begin(115200);
  delay(1000);

  dht.begin();
  Serial.println("DHT22 component test");
  Serial.println("Check wiring if you see failed readings.");
}

void loop() {
  if (millis() - lastReadTime < READ_INTERVAL_MS) {
    return;
  }
  lastReadTime = millis();

  float humidity = dht.readHumidity();
  float temperatureC = dht.readTemperature();
  float temperatureF = dht.readTemperature(true);

  if (isnan(humidity) || isnan(temperatureC) || isnan(temperatureF)) {
    Serial.println("Read failed: check DATA pin, pull-up resistor, power, and ground.");
    return;
  }

  float heatIndexC = dht.computeHeatIndex(temperatureC, humidity, false);

  Serial.print("Temperature: ");
  Serial.print(temperatureC, 1);
  Serial.print(" C / ");
  Serial.print(temperatureF, 1);
  Serial.print(" F  |  Humidity: ");
  Serial.print(humidity, 1);
  Serial.print(" %  |  Heat index: ");
  Serial.print(heatIndexC, 1);
  Serial.println(" C");
}

main/main.c

// ESP-IDF starter structure for this component.
// Keep the wiring from the pinout section, then move the read/write logic into app_main().

#include <stdio.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"

void app_main(void) {
  printf("DHT22 Temperature & Humidity Sensor ready\n");
  while (true) {
    // Add component read/write code here.
    vTaskDelay(pdMS_TO_TICKS(1000));
  }
}

The library include gives Arduino access to the DHT class. DHTPIN stores the ESP32 GPIO number connected to DATA, and DHTTYPE tells the library to use DHT22 timing.

setup() starts Serial Monitor and initializes the sensor. loop() uses millis() instead of delay() so the structure is easier to expand later with displays, buttons, Wi-Fi, or relays.

readHumidity(), readTemperature(), and readTemperature(true) request values from the sensor. isnan() catches failed reads before bad values enter the rest of your program. The final Serial.print() block formats the values so beginners can compare Celsius, Fahrenheit, humidity, and heat index on one line.

Expected Output

Open Serial Monitor at 115200 baud. A healthy circuit prints one line about every 2 seconds:

Temperature: 24.3 C / 75.7 F | Humidity: 55.0 % | Heat index: 24.1 C

The value should move slowly. Breathe near the sensor from a short distance and humidity should rise. Place it near a window and temperature may drift. If the output says "Read failed", the ESP32 did not decode a valid pulse train from the sensor.

Common Mistakes

Powering the module from 5 V while the DATA pull-up also goes to 5 V.
Using a bare DHT22 without the required pull-up resistor.
Reading faster than once every 2 seconds.
Wiring DATA to one GPIO but using a different pin number in code.
Forgetting to install Adafruit Unified Sensor with the DHT library.
Expecting DHT22 to behave like an analog sensor with analogRead().
Touching the sensor grill and warming it with your fingers.
Mounting the sensor directly above a warm ESP32 voltage regulator.
Using long loose jumper wires during breadboard testing.
Treating DHT22 readings as laboratory-grade measurements.

Troubleshooting

Problem	Possible cause	Solution
Serial Monitor prints "Read failed"	DATA pin mismatch, missing pull-up resistor, bad ground, or reading too fast.	Confirm DATA is on GPIO4, add a 10 k ohm pull-up for a bare sensor, share GND, and keep the 2 second interval.
Code will not compile because DHT.h is missing	The Adafruit DHT sensor library is not installed.	Install "DHT sensor library" by Adafruit and "Adafruit Unified Sensor" from Arduino Library Manager.
Upload works but no output appears	Serial Monitor baud rate does not match the code.	Set Serial Monitor to 115200 baud and press the ESP32 reset button.
Readings are stuck or always zero	Sensor is not powered, ground is missing, or the jumper is in the wrong breadboard row.	Check 3.3 V, GND, and breadboard rows with the board unplugged.
Temperature is higher than the room	Sensor is too close to the ESP32 regulator, USB chip, laptop exhaust, or your hand.	Move the sensor away from heat sources and wait several readings.
Humidity jumps when you breathe nearby	Human breath is warm and humid.	This is normal. For stable room readings, place the sensor away from your face and airflow.
Values update slowly	DHT22 is designed for slow environmental measurements.	Use a BME280 or SHT31 if you need faster or more stable readings.
ESP32 will not boot after wiring	The sensor is connected to a boot-sensitive pin or the wiring pulls a pin into the wrong state.	Use GPIO4 for this beginner circuit and avoid strapping pins such as GPIO0, GPIO2, GPIO12, and GPIO15 until you understand boot modes.
Readings work on USB but fail on battery	Battery voltage or regulator output is unstable.	Use a stable 3.3 V regulator and add a small decoupling capacitor near the sensor if wires are long.
Sensor works sometimes and fails sometimes	Loose jumper wires or breadboard contact resistance.	Reseat all wires, shorten the DATA wire, and avoid moving the breadboard while testing.
Humidity stays at 99 or 100 percent	Condensation, water exposure, or a damaged sensing element.	Let the sensor dry in clean room air. Replace it if readings do not recover.
Fahrenheit output looks wrong	Calling readTemperature(true) was removed or mixed with Celsius math.	Use readTemperature() for Celsius and readTemperature(true) for Fahrenheit.
Heat index seems close to temperature	Heat index changes strongly only when temperature and humidity are high.	This is normal at comfortable room conditions.
Library examples use another pin	Example sketches often use Arduino Uno pin numbers.	Change DHTPIN to the ESP32 GPIO you actually wired, such as 4.
Long cable gives unreliable readings	The one-wire timing signal is degraded by cable capacitance and electrical noise.	Use shorter cable, twisted ground/data pairing, a stronger pull-up such as 4.7 k ohm, or choose an I2C sensor for longer wiring.

Related Guides

Related Projects

FAQ

What does the DHT22 measure?

Is DHT22 digital or analog?

Can I connect DHT22 directly to ESP32?

Can I power DHT22 from 5 V?

Which GPIO is best for DHT22 on ESP32?

Why do I need a pull-up resistor?

What resistor value should I use?

How often can I read DHT22?

What does NaN mean?

Is DHT22 accurate?

Is DHT22 better than DHT11?

Is BME280 better than DHT22?

Can DHT22 be used outdoors?

Can it measure water temperature?

Can it measure soil moisture?

Why does humidity change when I breathe on it?

Why is the temperature too high?

Do I need a capacitor?

Can I use multiple DHT22 sensors?

Does DHT22 work with MicroPython?

Can I use interrupts with DHT22?

Why does Wi-Fi sometimes affect readings?

Glossary - What does DHT22 Temperature & Humidity Sensor mean in an ESP32 project?

Glossary - What is a signal pin?

Parent tips - Is DHT22 Temperature & Humidity Sensor safe for a beginner?

Parent tips - What should I watch during the build?

Teacher tips - How can DHT22 Temperature & Humidity Sensor fit into a classroom lesson?

Teacher tips - How should students be assessed?

Challenge yourself - What is a useful next step after DHT22 Temperature & Humidity Sensor works?

Challenge yourself - How can I prove I understand it?

Mini quiz - What should you check before changing wires?

Mini quiz - Why is common ground important?

Review, Testing, and References

Author: Abdul Mubeen and the ESP32 Engine editorial team. Last updated: 2026-07-05. Reviewed: wiring, code, beginner safety, and ESP32 compatibility. Educational level: Beginner.

Use this component page as an educational starting point. Check official documentation before using the part in production, high-current, outdoor, battery, or safety-critical hardware.

Downloads

DHT22 datasheet for electrical ratings, timing notes, and accuracy limits. Use it when designing classroom worksheets or production prototypes.

Download Datasheet (PDF)

DHT22 Temperature & Humidity Sensor

00Plain-English Overview

AWhere You Use It

01Quick Facts

How It Works

02Technical Specifications

03Pinout

04Wiring Diagram

05Code Examples

OKExpected Output

!Common Mistakes

06Troubleshooting

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